1. Field of the Invention
The present invention relates to layer-by-layer assembly of nanoparticles, particularly magnetic nanoparticles, into smooth, thin nanoparticles-containing films on a variety of sized and shaped substrates.
2. Description of the Related Art
Self-assembly of functional objects with controlled structure and lateral dimensions is of fundamental and technological interest. Self-assembly is a naturally-occurring process, an evident example being biological molecules, which self-organize into various living structures. The molecules will combine in various manners in this self-assembly process via weak van der Waals interactions, hydrogen bond interactions, or strong ionic and covalent bond interactions. The idea of this molecule-based, self-assembly approach has been applied to the fabrication of artificial structures with controlled functionality. A variety of patented processes based on ionic absorptions to form polymeric/organic films, organic/inorganic hybrid films, and chemical interactions to form polymeric/organic films, or organic/inorganic hybrid films have been issued.
Nanoparticles contain hundreds to thousands of single molecules or atoms and have long been recognized as having enhanced chemical and physical properties compared to their bulk forms. It was recently realized that these nanoparticles with uniformity in size, shape and internal structure could be used as unique building blocks to fabricate nanoparticles-based functional structures. Generally, this nanoparticles-based self-assembly is governed by the nature of the interactions exhibited among the stabilized particles. Various monodisperse nanoparticle materials, including polymers, semiconductors, and metals, have been tested for use in building self-assembly nanoscale devices.
Advances in magnetic recording technology have driven the development of new magnetic nanoparticle-based media/devices and have increased the need for uniformity in both particle size and particle magnetics. Self-assembly of magnetic nanoparticles may offer a suitable approach to such media. In these nanoparticulate films, grains (nanoparticles) are uniform and encapsulated in a non-magnetic coating which minimizes exchange coupling between adjacent grains. Such a new paradigm may present a magnetic recording medium, possibly supporting areal storage densities beyond Terabits per square inch. Until now, the chemical processes to control the assembly thickness and lateral dimension are mainly applied to non-magnetic nanoparticles. Controlled chemical assemblies of magnetic nanoparticles for magnetic recording applications are rare, and most of those processes focus on tape applications.
The present invention focuses on a process to assemble monodisperse nanoparticles on functionalized substrates and the structure resulting therefrom.
In view of the foregoing and other problems, disadvantages, and drawbacks of conventional magnetic storage devices, the present invention has been devised, and it is an object of the present invention, to provide a structure and method for a process that forms a multilayer nanoparticle thin film assembly. The process begins by functionalizing a substrate with functional molecules. Next, the invention replaces a stabilizer on a bottom surface of the first nanoparticles with the functional molecules via surface ligand exchange to make a first nanoparticle layer on the substrate. The invention then replaces the stabilizer on a top surface of the first nanoparticle layer with functional molecules via surface ligand exchange. The invention replaces the stabilizer on a bottom surface of the second nanoparticles with the functional molecules via surface ligand exchange to make a second nanoparticle layer on the first nanoparticle layer. Lastly, the invention repeats the previous steps and forms additional nanoparticle layers. The substrate can include either glass, quartz, ceramics, silicon, silicon oxide, or carbon. The functionalization of the substrate can include coating a layer of the functional molecules on the substrate by dipping the substrate into the molecule solution; or, it can include spin coating a layer of the functional molecules on the substrate. The functional molecules can either include monomeric or polymeric molecules; or it can include COOR, CONR2, NH2, SH, OH; or at least two functional groups represented as in H2Nxe2x80x94Rxe2x80x94NH2. The R comprises a common organic or inorganic chain. The stabilizer can be either H2O, RCOOR1, RCONR1, RNH2, RSH, RCN, ROH, or R4N+, where R and R1 represent common organic chains. After the functionalizing process, the invention performs a particle dispersion of aqueous alcoholic, ether, or hydrocarbon solvent. Next, the invention rinses the substrate with solvent and dries the substrate. The first nanoparticles and the second nanoparticles can be the same, or they can be different.
The invention also includes a process which forms a multilayer nanoparticle thin film assembly. First, the invention functionalizes a substrate with functional molecules. Next, the invention replaces a stabilizer on a bottom surface of the first nanoparticles with the functional molecules via surface ligand exchange to make a first nanoparticle layer on the substrate. The invention then replaces the stabilizer on a top surface of the first nanoparticle layer with functional molecules via surface ligand exchange. The invention replaces the stabilizer on a bottom surface of the second nanoparticles with the functional molecules via surface ligand exchange to make a second nanoparticle layer on the first nanoparticle layer. The invention repeats the process to form additional nanoparticle layers and then thermally anneals the multilayer nanoparticle thin film assembly to modify the magnetic and chemical properties of the thin film assembly. The thermally annealing process is performed under an inert atmosphere comprising either nitrogen, argon, or helium. This process is also performed under a reducing atmosphere that includes either hydrogen atmosphere, nitrogen and hydrogen atmosphere, argon and hydrogen atmosphere, or helium and hydrogen atmosphere. The thermally annealing process is also performed under a reactive gas atmosphere. The reactive gas comprises either air, oxygen, hydrocarbon, hydrogen sulfide, halogen or thermally annealing forms, respectively, being one of a granular metal oxide film, a metal carbide film, a metal sulfide film, or a metal haloride film.